279 
These difficulties may be overcome by a method of shadows 
in the following manner. 
Two rods R,M,, R,M, are screwed into the middle points 
of the opposite sides CD, AB of the Board, and their ends are 
connected with the rod R,2, so as to form the three sides of a 
parallelogram. The plane of this parallelogram by revolving 
about VM, as an axis may make any angle with the plane of 
the Board. FF, isa thread stretched parallel to RR, H,S are 
fixed points in the Board in the straight line M,M,. 
The thread R,Z meets FF, in q; SS, is a thread tightened 
by hand. is a candle placed im a vertical plane through q. 
The shadow of g, namely Q, will trace out a straight line, QL, as 
in the first method parallel to CD. The shadow of FF, will be 
QP parallel to AC; and the intersection of the shadows of R, £ 
and SS, 2.¢. p will be the required Perspective of P. 
Another method is represented below. The Board is sup- 
ported upon a stand which may be slid to any position by run- 
